alspe: 3-way or 2-way? Depends on how accurate you want the system to be. Personally I listen to a lot of music that was not recorded with audiophiles in mind, and so I do not mind if my system isn't perfect (I stopped obsessing over Audio Perfection years ago since I realized it was ruining my love for music and making this hobby too stressful!).
Lately I ran across several examples of 2 way systems without crossover on the bass driver.
One of the systems was 8 inch bass driver in ~20L sealed enclosure, no crossover on the bass, LR-2@~5kHz crossover on the tweeter.
It impressed me allot and I even did research on the impulse response of different crossovers.
The results are that virtually no crossover can handle a square wave impulse corectly, with Butterworth being the worst and Linkwitz-Riley being the best, but still it does not interpret it precisely. I used LTSpice, the internet and consulted an acoustic engineer.
And instantly, what seemed like a cost cutting measure became a desirable feature.
My conclusions are that since you can't avoid tweeter crossover, the best possible impulse response can be achieved with crossover only on the tweeter and the best performing and yet simple crossover is the LR-2. This combined with sealed bass enclosure gives several advantages which are unobtainable otherwise, this is lowest group delay, best impulse and transient response.
The science behind this is that an impulse (music is impulse character signal rather than sine or anything else) has a leading edge that can be considered both as a close approximation to DC or to infinitely high frequency. Thus it gets discriminated by the low pass crossover to different extent and is mistakenly recognized by the high pass crossover. The higher the high pass, the less such "mistakes" it will make. The most pronounced and in the same time most important impulses in music are related to the low frequencies and midrange frequencies below 1 khz. The crossoverless bass driver will see unaltered impulse shape as well as the associated continuation of the signal.
So, my aim with any driver for a 2 way, would be to find one that can be used without a crossover. The example that I investigated had a Le of 0.35 mh which when simulated gives an electrical -6 db point around 5 kHz. High Qms is advisable if you are after good impulse response, otherwise impulses could get "eaten". Low Fs and low Qts are to search for if you wish to oblige from the low group delay offered by the sealed enclosures.
Best Regards!
One of the systems was 8 inch bass driver in ~20L sealed enclosure, no crossover on the bass, LR-2@~5kHz crossover on the tweeter.
It impressed me allot and I even did research on the impulse response of different crossovers.
The results are that virtually no crossover can handle a square wave impulse corectly, with Butterworth being the worst and Linkwitz-Riley being the best, but still it does not interpret it precisely. I used LTSpice, the internet and consulted an acoustic engineer.
And instantly, what seemed like a cost cutting measure became a desirable feature.
My conclusions are that since you can't avoid tweeter crossover, the best possible impulse response can be achieved with crossover only on the tweeter and the best performing and yet simple crossover is the LR-2. This combined with sealed bass enclosure gives several advantages which are unobtainable otherwise, this is lowest group delay, best impulse and transient response.
The science behind this is that an impulse (music is impulse character signal rather than sine or anything else) has a leading edge that can be considered both as a close approximation to DC or to infinitely high frequency. Thus it gets discriminated by the low pass crossover to different extent and is mistakenly recognized by the high pass crossover. The higher the high pass, the less such "mistakes" it will make. The most pronounced and in the same time most important impulses in music are related to the low frequencies and midrange frequencies below 1 khz. The crossoverless bass driver will see unaltered impulse shape as well as the associated continuation of the signal.
So, my aim with any driver for a 2 way, would be to find one that can be used without a crossover. The example that I investigated had a Le of 0.35 mh which when simulated gives an electrical -6 db point around 5 kHz. High Qms is advisable if you are after good impulse response, otherwise impulses could get "eaten". Low Fs and low Qts are to search for if you wish to oblige from the low group delay offered by the sealed enclosures.
Best Regards!
There are a couple of major flaws with what you're trying to say here.
1) You're only considering the electrical transfer function of the crossover and completely ignoring the acoustic response. The acoustic response is all that matters in the end result, the electrical crossover transfer function is of academic interest only during the design process as a means to obtain the final acoustic response, which is the sum of electrical filter and driver transfer functions.
It's almost certain that the "woofer with no crossover" has an inherent mechanical low pass roll-off near the tweeters crossover frequency, (if the speaker is well designed) probably approximately 12dB/oct.
Therefore everything you say about the group delay, transient response and so on is incorrect as it is based on a faulty premise. The "woofer with no crossover" will have the transient response, group delay and so on which is applicable to whatever its natural low pass roll-off is, it is not magically avoiding the problems of crossovers - the woofer has a built in mechanical low pass filter.
2) Regarding square wave handling you say Linkwitz Reily is the best, in fact 1st order butterworth is the only one which will sum exactly to the original waveform. However this is of little relevance in speaker design as all the research says that correct waveform reproduction of square waves is not required or necessary, and that the phase shifts introduced by typical well designed crossovers (which distort square waves) are inaudible.
Correct square wave reproduction is one of those things that looks good on paper to an engineer but is not based on or backed up by any psycho-acoustic research, and designing a speaker that truly reproduces square waves almost inevitably results in severe compromises elsewhere in the performance. (Usually because it's attempted with time aligned 1st order crossover designs)
This doesn't make any sense to me. I'm not even sure what you're trying to say here...
As pointed out earlier, it doesn't matter what the bass driver "sees" at its input terminals, the acoustic response it radiates is all that matters. Unless the woofer can produce the entire audio spectrum to beyond 20Khz by itself it is altering the impulse shape due to its limited bandwidth. If it had this level of performance a tweeter would not have been necessary in the first place.
A few problems here.
The first is the suggestion that the Le of the driver is the only source of high frequency rolloff in a woofer - this is almost never the case. It's typically the mechanical performance of the cone that sets the upper frequency limit. Le may or may not contribute additional modest roll-off to the high frequency response, or it may actually prevent the drivers on-axis response from increasing with frequency (before eventually rolling off) due to beaming.
The second problem is that you don't seem to appreciate the fact that any roll-off contributed by Le is in fact an electrical low pass filter, thus negating your whole "woofer with no crossover" concept.
Thirdly, Le is not a "pure" inductance due only to the voice coil winding, part of it is electromechanical, therefore the roll-off that would be afforded is not as expected from a coil of the same inductance value.
(Plot the impedance vs frequency curve of a driver, then compare it to a resistor in series with an inductor, both of the same value as Re and Le of the driver, and you'll see they diverge at high frequencies)
Eaten ?
I don't understand what you're trying to say here.I'm not sure why you see high Qms and simultaneously low Qts as being important. Qms by itself really doesn't matter, except in its contribution to Qts....
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Eaten got my conclusions
For the last part, I made a shortcut in the presentation as I have skipped the reasoning for the low Qms which is to keep the box relatively small.
Anyway, a big thanks for the eye opening! I have observed only the electrical part of it, an error which should be avoided in the future.
The DC to infinity postulate obviously can't happen with a driver with limited bandwidth, it will limit it in the same way that a crossover would. Maybe it is strongly specific for each application.
Thank you again!
Then, I better ask.
What about the relation between the bandwidth, the crossover point and the impulse response?
Is it advisable to go for a higher crossover and thus for a driver that has bigger bandwidth based on all of the above considerations? Regardless of the rule of thumb, that it should be crossed over two octaves below it's upper limit or below it's cone breakup frequency. The last is applicable for second order, for higher or lower order it is less and more respectively.
Does the impulse response benefit from broader bandwidth of the bass driver?
What initiated the whole thinking is that the highpass crossover never shows even a close approximation of what is at the input.
See attached simulation.
tRise-0.0002ms, tFall-0.0002ms, tOn-0.0001ms; Total lenght is 0.0005 ms (approx. half of 1000hz impulse); Crossover is first order Butterworth at 1250 hz, 1.02mh, 15.9mf;
Green - input signal;
Blue - LF 8 ohm resistive load;
Red - HF 8 ohm resistive load.
And what bothers me is the shape of the HF signal.
Thanks in advance and sorry if the question is completely wrong. I apologize for the above conclusions.
For the last part, I made a shortcut in the presentation as I have skipped the reasoning for the low Qms which is to keep the box relatively small.
Anyway, a big thanks for the eye opening! I have observed only the electrical part of it, an error which should be avoided in the future.
The DC to infinity postulate obviously can't happen with a driver with limited bandwidth, it will limit it in the same way that a crossover would. Maybe it is strongly specific for each application.
Thank you again!
Then, I better ask.
What about the relation between the bandwidth, the crossover point and the impulse response?
Is it advisable to go for a higher crossover and thus for a driver that has bigger bandwidth based on all of the above considerations? Regardless of the rule of thumb, that it should be crossed over two octaves below it's upper limit or below it's cone breakup frequency. The last is applicable for second order, for higher or lower order it is less and more respectively.
Does the impulse response benefit from broader bandwidth of the bass driver?
What initiated the whole thinking is that the highpass crossover never shows even a close approximation of what is at the input.
See attached simulation.
tRise-0.0002ms, tFall-0.0002ms, tOn-0.0001ms; Total lenght is 0.0005 ms (approx. half of 1000hz impulse); Crossover is first order Butterworth at 1250 hz, 1.02mh, 15.9mf;
Green - input signal;
Blue - LF 8 ohm resistive load;
Red - HF 8 ohm resistive load.
And what bothers me is the shape of the HF signal.
Thanks in advance and sorry if the question is completely wrong. I apologize for the above conclusions.
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